1. Field of the Invention
The subject invention relates to swash plate axial piston pumps including condition responsive control of pump displacement.
2. Description of the Prior Art
In such pumps, the relative locations of the swash rotation axis, swash central axis of the swash device, and the plane containing the connection pivot points between the pistons and the swash device affect the performance characteristics of the pump such as maintaining clearance between the pistons and the valve plate and bias of the swash device to rotate to a higher or lower angle position. To increase the displacement of such a pump, the prior art typically employed three strategies: adding more pistons, increasing the diameter of the pistons, or increasing the diameter of the swash device to increase the stroke length of each piston. Each of these strategies necessarily increases the size and/or complexity to the pump, and therefore added cost or weight.
An example of an swash plate axial piston pump including condition responsive control of pump displacement is disclosed in U.S. Pat. No. 5,644,968 to Kimura. The '968 patent discloses a housing that has a piston block disposed therein which defines a plurality of piston bores. A piston is disposed and translational in each of the piston bores. A swash device defines a swash bore about a swash central axis and defines a swash rotation axis for rotation thereabout. A pivotal connection pivotally connects each of the pistons to the swash device for rotation about a connection pivot point during relative movement between the swash device and piston. The connection pivot points are aligned in a plane. A shaft is supported by the housing and passes through the swash bore and defines a shaft central axis. A hinge assembly pivotally supports the swash device about a hinge axis disposed on the opposite side of the plane from the piston block and is movable radially relative to the shaft central axis during relative movement of the swash device along the shaft. The swash rotation axis is offset from the plane away from the hinge axis and radially offset from the swash center axis away from the hinge axis to limit the clearance between the pistons and a valve plate disposed on the opposite side of the pistons from the swash device.
U.S. Pat. No. 5,253,576 to Bethke discloses a pump having a plurality of pistons and a swash device defining a swash center axis and a swash rotation axis. A pivotal connection connects each of the pistons to the swash device for rotation about a connection pivot point during relative movement between the swash device and the piston. The connection pivot points are aligned on a plane. A hinge assembly pivotally supports the swash device and is disposed on the opposite side of the plane from the piston block. The swash rotation axis is offset from the plane toward the hinge assembly and radially offset from the swash center axis toward the hinge assembly to bias the swash device to a higher angle position.